Four years ago, Charlotte Jones was a struggling actress frustrated by the lack of roles she was asked to play. This week her play, Humble Boy, opens at the Royal National Theatre, propelling her into a select band of women playwrights who have their work premiered on the South Bank.

"I feel rather guilty and ashamed that I became a writer so easily," says 32-year-old Jones. "I was never part of the 'trying to be a playwright' scene. But I think I paid my dues when I was acting - that's how I learned how to write. For some writers, going into a rehearsal room is a revelation, but not for me."

Some talents seem to spring fully- fledged from nowhere, and such is the case with Jones. Humble Boy - a Cotswolds-set comedy about astrophysics, bee-keeping and suicide, with strong echoes of Hamlet - is only her fourth stage play. Her first, Airswimming, a daffy feelgood comedy set in the most unlikely of places (an asylum for the criminally insane) got her noticed at BAC in 1997.

Her second, In Flame, dealing with the choices facing women both now and a century ago, got rave reviews at the Bush and transferred to the New Ambassadors. Her third, Martha, Josie and the Chinese Elvis won her the Pearson Television best new play award, and seems likely to be in the West End by Christmas.

Just four years after she first took up writing, Jones is shaping up to be one of Britain's most successful playwrights. Airswimming was her attempt to take control of her life after years of sitting waiting for her agent to call. She joked to friends that the women incarcerated in the asylum, hoping for news of a release, were actually Jones the actress sitting by the phone waiting for it to ring.

At the very least, she thought she would write herself a good part, and duly cast herself as one of the two leads in Airswimming. It was to be the last time she was to appear on stage. Those unhappy years as an actress may be behind her now, but their legacy remains in her plays, which are notable for the meaty roles they provide for the entire cast.

"I can't write walk-on parts, probably because I played so many myself. All my characters have a journey. I am obsessed with character, and that's where I begin every play." In fact, Humble Boy begins with the image of a human resembling a bumblebee, and the theory that the body shape of the bumblebee should make flight aerodynamically impossible.

More than that, Jones wrote the play with a specific actor in mind - Simon Russell Beale, who she thought would be perfect for the role of astrophysicist Felix Humble. He returns to his family home for the funeral of his bee-keeping father, James, and discovers his mother Flora canoodling with a local bigwig. The only problem was that Jones didn't actually know Russell Beale.

But she struck lucky. Jones's husband, the actor Paul Bazely, was cast to play Guildenstern in John Caird's production of Hamlet, starring Russell Beale. Some weeks into rehearsal, Bazely thrust a copy of the play into his hand and said: "My wife has written this for you." Russell Beale wanted to do it and gave it to John Caird, who smoothed its path to the Cottesloe.

Not surprisingly, Russell Beale thinks Jones is the bee's knees. "You can't help but be flattered if someone writes a part for you," he says. But the more he works on the play, the more impressed he is by it. "My first instinct was that it was quite an old-fashioned play, but it's not. It is quite heightened, not naturalistic, and she is really savage about people. Both Felix and Flora are quite unpleasant. I love its ambition. There aren't many playwrights bold enough to relate personal relationships to cutting-edge theoretical physics."

Except perhaps Tom Stoppard. The structural similarities of Jones's In Flame to Stoppard's Arcadia, a play Jones hadn't even seen when she wrote In Flame, was remarked upon by some critics. Inevitably, Jones's playful use of super strings, quarks and neutrinos in Humble Boy will allow for further comparisons.

"I am quite flattered by the comparison. You'd be a fool not to be," says Jones, who is more irked by the way she gets lumped together with other women writers. She recently turned down a proposed feature that would have had her and another female playwright in a joint interview.

"No newspaper would think it a sensible idea to put Patrick Marber and Mark Ravenhill together, so why do it with women playwrights? It is marginalising to think of yourself as a woman writer. Who wants to be appreciated as a minority?"

The signs are that Jones's talent is increasingly being recognised by the vast majority, and Humble Boy won't do her reputation any harm. With success, though, comes added pressure. "As soon as you have any success, there are deadlines to meet, commissions to be fulfilled, and it gets harder and harder to write. But I am not stopping now. I couldn't. Not long ago, I heard another playwright say that the reason he wrote was because he had so many things to say. I don't feel like that at all. I don't think I've got lots of things to say. I just want to tell stories. Maybe that makes me a reactionary." She grins defiantly: "Well, if it does, I don't care."

 Humble Boy is at the Royal National Theatre from August 2. Box office: 020-7452 3000.